Zoiper 5.5.10

Perform voice and video calls using any VoIP provider or PBX components. Set up the standard parameters of the streaming video, including its resolution, rendering, and other configurable aspects. Integrate the client with Internet browsers and mail clients such as Outlook, Lotus Organizer, Thunderbird, etc.

Zoiper (an evolution of Idefisk) is a small and easy to use softphone application compatible with IAX and SIP protocols. It allows configuring multiple SIP/IAX accounts and has multiple lines (up to six simultaneous calls).

It has all the features expected in a softphone, like for instance an address book, hold, transfer, conference, and voicemail buttons. Additionally, it has a send fax option (it supports T.38 fax over IP), and compatibility with lots of PBX and Voip Service providers through its SIP and IAX profiles.

This softphone has a very simple interface but it allows for advanced configurations. It supports the following codecs: u-law, a-law, GSM, iLBC 20 and 30, speex, and G729 (with an additional cost). There are versions available for Windows, Linux, and Mac.

ZoIPer supports the following languages: English, German, French, Spanish, Dutch, Portuguese, Russian and Japanese

I definitely recommend this software for advanced users and for enterprises.

It can be downloaded as a demo (less features) for free and upgraded through a commercial license.